The discovery of ceramic-based high-temperature superconductor (HTS) materials during the 1980's opened the possibility of applying superconducting technology to electric power devices such as transmission cable, transformers, motors, and generators. The ‘high’ in HTS refers to the ability to achieve the superconducting state at temperatures attainable using inexpensive liquid nitrogen, rather than the liquid helium required by the ‘low’ temperature superconductors (LTS). Nitrogen gas, when cooled, condenses at −195.8° C. (77.36 K) and freezes at −209.86° C. (63.17 K), while helium gas condenses at −268.93° C. (4.2 K) and does not freeze at atmospheric pressure.
Due to superconductivity, an HTS conductor has resistive losses that are decreased to almost negligible levels. Achieving the decreased resistive losses now costs less since the higher temperatures significantly reduce the costs of cryogenic systems that cool the HTS conductor. This is a fundamental advance in wire technology; however, to date, only short HTS conductor samples have been fabricated at high performance levels. Contributing to this challenge is that, in the field of HTS conductors for power applications, the superconducting materials must be biaxially textured to assure large critical current densities.
An ion-beam-assisted deposition (IBAD) process is one method presently used to form HTS conductors. In an IBAD system, a biaxial texture is imparted to a template layer, for example, yttrium stabilized zirconium (YSZ) or magnesium oxide (MgO) that is formed on a tape substrate.
In an IBAD system, a coating is deposited on a substrate from a plume generated from a deposition source, while at the same time, an ion beam bombards the coating to impart a preferred characteristic to the deposited material. Traditionally, in an IBAD system used for an HTS conductor, an ion beam sputtering source has been used to generate the plume. A major disadvantage of such an IBAD system used for manufacturing an HTS conductor is that the size of available ion beam sputter sources are limited to about 0.6 m. In order to manufacture a conductor having lengths exceeding meters, kilometers, and even hundreds of kilometers, long production runs would be needed. Another disadvantage with using an ion beam sputtering system is that deposition rates are limited to about 1 angstrom per second (Å/s). Solving the problem of the small deposition zone and low deposition rates would remove the obstacle of slow throughput to lower costs with increased throughputs.
An alternative might be an IBAD system relying on an electron beam (e-beam) to vaporize an evaporant material; however, this solution is limited to short production runs. One of the components that limits longer production runs is the source of the e-beam, specifically the thermionic filament, which emits the thermal electrons that are accelerated into the beam. Like a filament in a common light bulb, thermionic filament has a finite lifetime. The lifetime is especially limited in an environment with gasses such as, for example, oxygen, that oxidize or corrode the filament. Solving the problem of that finite lifetime without shutting down production would remove one obstacle to continuous production runs of a week or more.
Thus, there remains a need for a new and improved tape-manufacturing system that has increased production throughput, while at the same time is capable of continuously coating the surface of long tape substrates with a minimum of interruptions.